Additional Balance Sheet and Cash Flow Information (Narrative) (Detail) - USD ($) $ in Thousands	9 Months Ended
Sep. 25, 2016	Sep. 27, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Gross unrealized gains (losses)	$ (140)	$ (467)
Gross unrealized gains (losses), net of taxes	$ (88)	$ (294)
Contractual maturities period of marketable securities (in months)	7 months

This item represents the pretax change in net unrealized holding gain (loss) on available-for-sale securities that has been included in accumulated other comprehensive income, a separate component of shareholders' equity, during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563

Name:	us-gaap_AvailableForSaleSecuritiesChangeInNetUnrealizedHoldingGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration